Empty/load valves are well known in the art. See, for example, U.S. Pat. Nos. 1,615,366; 4,648,661; 4,775,197 and 4,826,259. In general, such valves include a measuring arm responsive to movement of a part of the vehicle movable toward the wheels of the vehicle with load on the vehicle and valves controlled by the measuring arm for diverting air to a storage tank or canister when the load on the vehicle is light, e.g. the vehicle is empty or only lightly loaded.
In some of the present installations, the canister is welded to the car body whereas the measuring arm is on, and the valves it controls are in, a valve body which is secured to the canister by bolts or studs with nuts. Therefore, the valve body can be removed relatively easily, but removal of the canister is difficult and expensive and may require repairs of the supporting member after removal of the canister.
The canister used with an empty/load valve of one manufacturer usually is satisfactory with respect to some of its characteristics, e.g. volume, number of air ports and placement, for use with the empty/load valve of another manufacturer. However, the placement of air ports of the canister and the attaching parts of a canister manufactured by one manufacturer usually does not permit mere replacement of the empty/load valve of one manufacturer by the empty/load valve of another manufacturer. On the other hand, there is a need to be able to replace one valve by another of a different construction, e.g. when an improved valve is developed or the valve to be replaced has been found to be unsatisfactory for various reasons.
Accordingly, there is a need for a simple and inexpensive way of replacing an installed empty/load valve body of one structure with an empty/load valve of a different structure without removing the canister.
Furthermore, for the reasons set forth hereinafter, it has been found useful in the field to be able to determine visually, after the empty/load valve is installed, whether or not the canister contains air under pressure. Many canisters already installed do not have an indicator thereon for such purpose.